SiC, which is superior to Si or the like in, for example, heat resistance and electrical characteristics, has attracted attention as a new semiconductor material.
A semiconductor device made of SiC is manufactured by using a SiC substrate with a diameter of 4-inch or 6-inch, for example. A method for isolating the semiconductor element by using grooves preformed on the SiC substrate in which ion implantation, ion activation and electrode formation, and the like are performed thereon has been conventionally known as a method for manufacturing the plurality of semiconductor elements from one SiC substrate.
The SiC substrate may have grooves for the purpose of embedding of a MOSFET gate, in addition to the purpose of isolation of the semiconductor element (see a trench gate MOSFET, NON-Patent Document 1).
Here, the SiC substrate needs to be heat-treated for activating ions after implanting ions such as Al, or the like. The heat treatment (ion activation treatment) needs to be performed at a high temperature of 1500° C. or more. However, when ion implantation treatment and ion activation treatment are performed on the SiC substrate, the surface of the SiC substrate is roughened.
Therefore, a carbon cap method in which a surface roughness of the SiC substrate is prevented by forming a carbon cap on the SiC substrate is used. In the carbon cap method, a resist is applied on the surface of the SiC substrate and then the SiC substrate is rotated around a perpendicular line of the surface as a rotation shaft, which can make the resist uniform (spin coating process). Then, the carbon cap is formed by carbonizing the resist. Formation of the carbon cap can suppress the surface roughening of the SiC substrate which is occurred during ion activation treatment. After ion activation treatment, the treatment for removing the carbon cap is needed.